Dirty region for fullscreen video

I have done this on top of #2309, only this commit bc222985ae076d2bb9fc21250a1123d86b323a4e is relevant for this pr.

Video rendering is moved from application to GUIWindowFullScreen. The window checks if something should be rendered and sets the dirty flag accordingly.
Embedded platforms like the RPi which use bypass method benefit from this. The main thread won't flip if the gui is not shown and no subs are to be rendered.

Thoughts?